The long range objectives of our research are to gain an insight into the mechanisms operative in the regulation of RNA synthesis in eukaryotic organisms, emphasizing higher plants, and to assess the role of hormone-regulated RNA synthesis in the induction of tissue proliferation. The work currently in progress and to be continued during the next year emphasizes 1) an analysis of the mechanisms operative in the rapid modulation of RNA polymerase I activity during various normal and hormone-induced growth transitions and 2) an analysis of the nucleotide sequence complexity of RNAs (total and poly(A) RNAs and polyribosome-associated mRNA) in control and hormone-treated tissues. Standard procedures of enzymology, DNA-RNA hybridization, cell fractionation, and the study of regulatory molecules will be used. We hope to eventually integrate the results of these studies into an analysis of the relationship of rRNA synthesis, ribosome formation, and ribosome function to the onset of tissue proliferation.